Since last week, the agency said it had confirmed two additional deaths in Colorado and one in Kansas. Previously, the agency had reported five deaths in New Mexico, three in Colorado, two in Texas and one death each in Kansas, Missouri, Nebraska, Oklahoma and Maryland.

The outbreak is the deadliest in the U.S. in more than a decade - and the death toll may continue to rise. Wyoming's state health department said it had confirmed a Listeria death in that state, though the CDC did not include that case in its count. Symptoms of listeriosis can take up to two months to show up, and more illnesses are expected.

The CDC has reported illnesses in Alabama, Arkansas, California, Colorado, Idaho, Illinois, Indiana, Kansas, Maryland, Missouri, Montana, Nebraska, New Mexico, North Dakota, Oklahoma, Texas, Virginia, West Virginia, Wisconsin, and Wyoming. Colorado has the most illnesses with 30, while Texas has 14 and New Mexico has 13.

Jensen Farms of Holly, Colo. recalled its cantaloupes Sept. 14 after the farm's melons were traced to the Listeria illnesses. The farm says it shipped cantaloupes to 28 states, though the FDA has said it may be more. Illnesses have been discovered in states that were not on the shipping list and company officials have said the product is often resold, so it's hard to track.

FDA Commissioner Margaret Hamburg said Tuesday that the agency is still investigating the cause of the outbreak. Officials have said they are looking at the farm's water supply and possible animal intrusions among other things in trying to figure out how the cantaloupes got contaminated. Listeria bacteria grow in moist, muddy conditions and are often carried by animals.

Most of the contaminated melons should now be out of the food supply. The farm last shipped its cantaloupes on Sept. 10, and their shelf life is about two weeks. Officials from the CDC and the FDA say any cantaloupes not from Jensen Farms are safe to eat.

The recalled cantaloupes may be labeled "Colorado Grown," "Distributed by Frontera Produce," "Jensenfarms.com" or "Sweet Rocky Fords." Not every recalled cantaloupe is labeled, the FDA said.

Government health officials said this is the first known outbreak of Listeria in cantaloupe. Listeria is generally found in processed meats and unpasteurized milk and cheese, though there have been a growing number of outbreaks in produce.

A rare disease, listeriosis usually only affects about 800 people a year, according to the CDC. But it is more deadlier than well-known pathogens like salmonella and E. coli, killing up to one in five people it affects.

Most healthy adults can consume Listeria with no ill effects, but it can kill seniors and those with compromised immune systems. It is also dangerous to pregnant women because it easily passes through to the fetus. The CDC said the median age of those sickened is 79.

Symptoms include fever and muscle aches, often with other gastrointestinal symptoms.